Hard disk drive incorporating rotating magnetic disks is commonly used for storing data in the magnetic media formed on the disk surfaces, and a movable slider including read sensors are generally used to read data from tracks on the disk surfaces.
Presently, MR sensor is used as a kind of popular read sensor because of its better capability to read data from disk surface at a greater track and linear densities than traditional film inductive slider.
Now, several types of MR sensors have been widely used by disk drive manufacturers in succession. One is anisotropic magnetoresistive (AMR) sensor, which makes the angle between the magnetization direction and the direction of sense current flowing through the MR element change and, in turn, cause a change the resistance of the MR element and a corresponding change in the sensed current or voltage. Another type is giant magnetoresistive (GMR) sensor manifesting the GMR effect. The GMR effect is a phenomenon that the magnetoresistive ratio (MR ratio) will change under an external magnetic field. The GMR sensor comprises two ferromagnetic layers and a non-ferromagnetic layer sandwiched between the two ferromagnetic layers. The resistance of the non-ferromagnetic layers varies with the magnetic moments of the ferromagnetic layers, the conduction electrons and the spin-dependent scattering. Still another type of MR sensor is tunnel magnetoresistive (TMR) sensor, which has become the mainstream MR sensor due to its more remarkable change of MR ratio by replacing AMR sensor and GMR sensor.
As shown in FIG. 1, a TMR sensor 500 with a rectangular MR element includes two magnetic layers 503, 505, a tunnel barrier layer 504 sandwiched therebetween, two electrode layers 502, 506 to sandwich the magnetic layers 503, 505, and a substrate 501 to hold the above layers. When a current is fed to the magnetic layers 503, 505, a tunnel current passing through the tunnel barrier layer 504 will change according to the relative angle between magnetization directions of the two magnetic layers 503, 505. Thus the recorded data can be read from a magnetic medium because the signal field causes a change of magnetization direction of the two magnetic layers, which in turn causes a change in resistance of the TMR sensor.
However, big thermal noises and low read sensitivity problems always exist in the above-mentioned MR sensors and influence their working performance seriously.
For solving thermal noise problems, an improved MR sensor is disclosed in JP patent publication application No. JP 2000-200404. As illustrated in FIG. 2, a trapezoidal MR element 10 of the MR sensor has a narrower top edge 37 and a wider bottom edge 27 facing air bearing surface (ABS) 21. A pair of hard magnets 11 is respectively placed at the side of the MR element 10. The hard magnet 11 provides a longitudinal bias field to the MR element 10, which has a magnetic direction 12. As known, in the area of the MR element near the hard magnet 11, the longitudinal bias is stronger than the area far from the hard magnet 11, and a stronger longitudinal bias is helpful for decreasing thermal noises. As shown in FIG. 2, a hatched portion of the trapezoidal MR element 10 indicates a stronger longitudinal bias area, and the other portion is a weak longitudinal bias area. Comparing with the rectangular MR element of the traditional MR sensor, the weak longitudinal bias area of the trapezoidal MR element 10 is reduced under a same width of the bottom edge and a same height of MR element (MR height). Thus, the thermal noises of the whole MR element and then the MR sensor are reduced. Unfortunately, because the bottom edge 27 facing ABS is still wider, a high read sensitivity is difficult to attain.
In order to solve the problem, referring to FIG. 3, another MR sensor is disclosed in JP patent publication application No. JP 6-215333. As shown in FIG. 3, a MR element of the MR sensor comprise a trapezoidal track width restriction layer 61 which has a wider edge 62 and a narrow bottom edge 63 facing ABS 65. For the sensing area, its magnetization direction is generally parallel with the magnetic layer, and its signal magnetic field decreases gradually with increasing of the distance from the ABS. Comparing with the trapezoidal MR element 10 shown in FIG. 2, since the sensing area facing the ABS becomes narrower under a same total sensing area, thus when a same current is provided, a big current density crossing the sensing area near the ABS is attained, and then a higher read sensitivity will be obtained.
As well known, lapping process of the MR element is a very important process in the manufacturing process of a slider. That is, the edge of the MR element facing the ABS, such as the bottom edge 27 shown in FIG. 2 or the bottom edge 63 shown in FIG. 3, is required to be lapped so as to achieve a predetermined MR height. However, since the above-mentioned trapezoidal MR elements both has a wider bottom edge being lapped, so the lapping process of the bottom edge is difficult to control, and making the MR height difficult to control.
For a slider with MR sensor, a narrower and denser data track of the disk is required so as to attain an increased recording density. So it is desired for reducing the size of the sensor incorporated in the reducing slider. That is, the track width rests with the width of the MR element facing ABS, if the width of the MR element is too big, the track width is increased and, in turn, decreasing the data track density, which affects the read performance of the slider. However, reducing the size of the sensor (namely the width of the MR element, MR height, and total sensor area) will effect on the performance of the sensor. For example, if the sensor area is too small, the resistance area is decreased to cause reliability of the MR sensor become poorer. At the same time, the current density crossing the sensor area is increased to bring electro-static discharge (ESD) problem. In one word, it is a big problem to solve for existing MR sensor.
Hence, it is desired to provide an improved MR sensor for a slider to overcome the above-mentioned drawbacks.